The use of polyether fluids is well known in applications such as hydraulic fluids, brake fluids, cutting oils and motor oils where the synthetic ability to structure properties such as water miscibility, fire resistance, lubricant properties and extreme pressure resistance provides a competitive advantage over other fluids. The polyether oils in practical use comprise polyalkylene glycols and their end-capped monoethers, diethers, monoesters and diesters. They include polyalkylene oxide polyether homopolymer, copolymer and block copolymer and can be prepared principally by the anionic polymerization or copolymerization of oxiranes or epoxides. Small or large molecule end-capping groups are added in the polymerization to modify the properties of the resultant polyether as appropriate for the selected application.
Basic catalysts are generally employed in the art for the production of polyethers from cyclic ethers such as oxiranes because anionic catalysis produces a product with a substantially smaller or narrower molecular weight distribution than the product produced by cationic polymerization using conventional Lewis acids. Lewis acids are intrinsically of higher activity leading to extensive chain transfer and cyclic formation reactions. Also, effective acid catalysts for cyclic ether polymerization or copolymerization including liquid super acids such as fuming sulfuric acid, fluorosulfonic acid or BF.sub.3 /promoter catalysts are difficult to handle and are more troublesome to dispose of in an environmentally acceptable manner.
These activity and environmental issues are of great concern for the production of tetrahydrofuran-containing polyethers which employ acid catalysts. Substantial efforts in the prior art have been devoted to resolving these issues by preventing cyclic formations and by employing solid acid catalysts.
U.S. Pat. No. 4,568,775 describes a two phase process for the polymerization of tetrahydrofuran or a mixture of tetrahydrofuran and other cyclic ethers in contact with a heteropolyacid catalyst having 0.1 to 15 mol of water per mol of heteropolyacid catalyst present in the catalyst phase. The polyether glycols prepared from the process are useful as starting material for the production of urethane. The process uses large volumes of catalyst in the two phase process.
U.S. Pat. No. 4,988,797 polymerizes oxetan and tetrahydrofuran (THF) in the presence of excess alcohol in contact with acid catalyst wherein the molar ratio of acid catalyst to hydroxyl groups is between 0.05:1 and 0.5:1. The invention is particularly directed to the polymerization of oxetanes.
U.S. Pat. No. 5,180,856 teaches the polymerization of THF and glycidyl ether in the presence of alkanol to produce polyethers. Lewis acid catalyst such as boron trifluoride is used. The polymerization is carried out in the presence of 0.01-5 weight percent of Lewis acid catalyst. The products are useful as lubricants. The Lewis acid catalysts that are dissolved in the polyether-products have to be separated, destroyed and discarded as wastes.
U.S. Pat. No. 4,481,123 teaches the production of polyethers from THF and alpha alkylene oxides having an alkyl radical containing 8-24 carbon atoms. The polymerization is carried out in contact with Lewis acid catalyst. The polymerization can further include C.sub.1 -C.sub.4 epoxide and alcohol. The polyether products are useful as lubricants.
In view of the excellent lubricant properties of polyethers and the known advantages of many non-polar hydrocarbon fluids, including synthetic hydrocarbon fluids (SHF's), and particularly polyalpha-olefins (PAO) or severely hydroprocessed basestocks of 3-100 cSt viscosity at 100.degree. C., one is compelled to consider blends of these components to form lubricants with enhanced performance capabilities. Polyether blends with mineral oil lubricants are known and useful in the art. However, attempts to form such blends with non-polar basestocks has been frustrated by the poor solubility of polyethers in SHF's.
High molecular weight or high viscosity SHF's such as 40 or 100 cSt PAO are highly hydrophobic. Because of this hydrophobicity they are poor solubilizers for many polar or slightly polar lubricant base stocks and additives. It is not obvious to one skilled in the art how to determine the solubility trends for such highly hydrophobic fluids toward polar organic molecules. For instance, dicarboxylic esters were used as blend stocks for 40 or 100 cSt PAO; but other esters such as polyol esters with similar hydrocarbon compositions were immiscible.
Recently, severely hydrotreated basestocks have become available to the lubricant formulator. Severely hydrotreated base stocks are described in the article "Base Stocks: The Real Story" by D. E. Deckman et al in Hart's Lubricant World, pp 46-50, July 1997, which article is incorporated herein by reference. These base stocks, typically produced by hydrocracking distillate or wax, have improved oxidation stability and very low olefins and aromatics content. However, due to the severity of the hydroprocessing of the feedstock the resulting base stocks are very paraffinic and have poor or decreased solubility and compatibility with polar fluids such as polyalkylene glycols. In order to take advantage of the performance features of both the polyethers and the severely hydroprocessed base stocks polyethers are required that have increased solubility and compatibility with severely hydrotreated basestocks.
It is also well known in the literature of lubricant arts that the chemical compositions of conventional mineral oil produced from solvent refining are very different from SHF such as polyalphaolefins or severely cracked base stocks. These compositional differences are responsible for many of their property differences such as their solubility with additives or polar cobasestocks, oxidative stability, etc. However, the different compositions of SHF and severely hydrotreated base stock compromise their ability to solubilize polyether additives and so, absent the discoveries of the instant invention, have denied to the lubricant formulator the use of the performance advantages that can accrue to a SHF or severely hydrotreated base stock that incorporate polyethers as additive or cobasestock.
U.S. Pat. No. 4,481,123 teaches new polyethers obtainable by polymerization of 1,2-epoxyalkane with 8 to 26 carbon atoms and a tetrahydrofuran in the presence of a hydroxy compound. The polymerization is catalyzed by conventional Lewis acid catalysis to produce lubricants that are miscible with mineral oil. This result is not unexpected for conventional mineral oils are usually much more polar than synthetic hydrocarbon fluids such as PAO and more polar than severely hydroprocessed basestock. Conventional mineral oils typically contain 5-10% polar aromatic components and higher amounts of cyclic naphthenic components. As SHF's or severely hydroprocessed basestocks are essentially absent of these solubilizing components, their miscibility and compatibility with polyethers is restricted. Notably, the patent does not teach or claim that the new polyethers are, in fact, miscible with high viscosity SHF's; nor does the patent teach polymerization of polyethers by heteropolyacid catalysis.
It is an object of the present invention to provide polyether lubricants and a method for their preparation wherein the polyether lubricants are miscible with the relatively non-polar synthetic hydrocarbons, especially PAO and severely hydroprocessed basestock.
It is a further object of the present invention to provide blends of polyether lubricants and high viscosity PAO wherein the blends exhibit low pour point, high viscosity index (VI), superior antiwear properties, plus low friction coefficients.